1. Field of the Invention
This invention relates generally to an apparatus for transferring, storing and recovering hydrogen from a hydridable material and more particularly to such an apparatus used for transferring hydrogen under pressure while simultaneously removing any gaseous impurities from the hydrogen stream before the hydriding step.
2. Background Art
Hydrogen in the combinant form of water has long been employed in many chemical processes. Recent advances have permitted use of elemental hydrogen in gaseous form in physical processes, such as in heat transfer and electrical energy storage. For example, the fuel cell industry, among others, is continually developing new applications for hydrogen, including fuel cells and heat transfer applications. As a result there is a growing need to store hydrogen safely and conveniently in such applications.
Hydrogen has been stored conventionally as a gas in steel cylinders at high pressures over 2000 psi and at lower pressures as a liquid in insulated containers at very low temperatures. Both methods of storage require comparatively bulky storage containers that are often in need of maintenance. In addition to their unwieldy size, such containers are inconvenient due to the high pressure required for gas storage in cylinders, which can contribute to the possibility of hydrogen gas leakage from the cylinders.
Storage of hydrogen in metallic compounds and alloys, commonly called hydrides, has been recognized as a solution to the problem of hydrogen volatility and safe storage and delivery. Metal hydrides, in the form of metallic powder, can store large amounts of hydrogen at low pressures in relatively small volumes. Low pressure storage of hydrogen is relatively safe and allows the construction of hydrogen storage and delivery containers having forms significantly different than those presently known. Although the weight of the metal hydride powder is a consideration, there may result a concomitant reduction in the weight of the container, since excessively large pressures will not be encountered, and thick container walls are not as significant.
Including use in the storage of hydrogen, metal hydrides are also currently being evaluated for a variety of applications, including for gas compression, solar heat storage, heating and refrigeration, hydrogen purification, utility peak-load sharing, deuterium separation, electrodes for electrochemical energy generation, pilotless ignitors and internal combustion engines.
The processes and equipment used in hydrogen storage is the subject of several commonly assigned U.S. patents, for example, U.S. Pat. Nos. 4,396,114; 5,250,368; 5,532,074 and 5,688,611, the disclosures of which, where appropriate, are incorporated by reference as if fully set forth herein.
An important consideration, particularly addressed in U.S. Pat. Nos. 4,396,114 and 5,688,611, is the delivery of the hydrogen gas between the metal hydride material in a container, usually in powder form, and the end use equipment that utilizes the hydrogen gas, for example, a hydride compressor.
One difficulty that has been investigated is high stress due to the compaction of the powder and expansion thereof during hydride formation. These stress forces are directed against the walls of the storage container and may damage the container itself or the associated internal assemblies unless provision is made to accommodate the impact of the forces. The stress within the powder has been observed to accumulate until the yield strength of the container is exceeded whereupon the container plastically deforms, buckles or bulges and eventually ruptures. Such rupture may become dangerous since a fine, often pyrophoric powder may be expelled by pressurized, flammable hydrogen gas. Small, experimental cylinders of the aforedescribed type have indeed been found to open and burst when subjected to repetitive charging-discharging cycles, because of repeated and progressively more invasive structural and compressive stresses. Additionally, it is undesirable for containers to lose their integrity since any hydrogen stream expelled out of a hydride container may be subject to combustion with possibly catastrophic results.
While the solution to the problem of hydride powder compaction described in the above-described patents are normally adequate to control excessive bulging and deformity of the container by absorbing the stress of metal hydride particles expanding as hydrogen is absorbed therein, that solution has been found to lead to unintended and undesirable results when the hydride materials are subjected to numerous hydrogen absorption/desorption cycles. That is, as the hydriding cycles continue, minute amounts of hydride material become forced into the spaces between the spring loops, eventually forcing themselves between adjacent loops of the spring steel and entering the central conduit through which the hydrogen gas is intended to flow. This reduces flow efficiency, and if enough hydride material is injected into the conduit, blocks hydrogen flow, thereby defeating the purpose of the spring elements. What has been found necessary, therefore, is an inexpensive means for accommodating the stress forces resulting from hydrogen absorption/desorption phenomena, while simultaneously filtering from the gaseous hydrogen the gaseous impurities before the absorption process commences at the metal hydride surface, and also inhibiting the entry of hydriding material into the conduit defined by the springs.